One of the principal mechanisms by which cellular regulation is effected is through the transduction of extracellular signals across the membrane that in turn modulate biochemical pathways within the cell. Protein phosphorylation represents one course by which intracellular signals are propagated from molecule to molecule resulting finally in a cellular response. These signal transduction cascades are highly regulated and often overlapping as evidenced by the existence of many protein kinases as well as phosphatases Phosphorylation of proteins occurs predominantly at serine, threonine, or tyrosine residues and protein kinases have therefore been classified by their specificity of phosphorylation site i.e. serine/threonine kinases and tyrosine kinases.
Because phosphorylation is such a ubiquitous process within cells and because cellular phenotypes are largely influenced by the activity of these pathways, it is currently believed that a number of disease states and/or disorders are a result of either aberrant activation or functional mutations in the molecular components of kinase cascades. Consequently, considerable attention has been devoted to the characterization of these proteins.
PDK-1 (also known as PDPK-1, 3-phosphoinositide-dependent protein kinase-1, PtdIns(3,4,5)P3-dependent kinase-1, PKB kinase) is a recently isolated protein kinase which serves as a multifunctional effector downstream of phosphatidyl inositol 3-kinase. PDK-1 was first identified by its ability to phosphorylate the proto-oncogene, Akt-1 on residue Thr308 (Alessi et al., Curr. Biol., 1997, 7, 261-269; Stokoe et al., Science, 1997, 277, 567-570). It was demonstrated that this activation/phosphorylation only occurred in the presence of the lipids PtdIns(3,4)P2 or PtdIns(3,4,5)P3 resulting in the translocation of PDK-1 to the plasma membrane (Anderson et al., Curr. Biol., 1998, 8, 684-691). It has since been shown to phosphorylate the p70 S6 kinase in vitro and in vivo (Alessi et al., Curr. Biol., 1997, 7, 776-789) as well as various isoforms of protein kinase C (Le Good et al., Science, 1998, 281, 2042-2045).
Phosphorylation of these target proteins by PDK-1 mediates several normal processes within the cell including the metabolic effects of insulin, the induction of differentiation and/or proliferation, protein synthesis, apoptosis and stress responses (Alessi and Cohen, Curr. Opin. Genet. Dev., 1998, 8, 55-62; Cohen et al., FEBS Lett., 1997, 410, 3-10; Downward, Curr. Opin. Cell Biol., 1998, 10, 262-267; Staal et al., Genomics, 1988, 2, 96-98). Furthermore, the activation of Akt-1 has been associated with primary human gastric carcinoma (Staal, Proc. Natl. Acad. Sci. USA, 1987, 84, 5034-5037), prolymphocytic leukemias, and mixed lineage childhood leukemias (Staal et al., Genomics, 1988, 2, 96-98).
Currently, there are no known therapeutic agents which effectively inhibit the synthesis of PDK-1. Consequently, there remains a long felt need for agents capable of effectively inhibiting PDK-1 function. Antisense technology is emerging as an effective means for reducing the expression of specific gene products and may therefore prove to be uniquely useful in a number of therapeutic, diagnostic, and research applications for the modulation of PDK-1 expression.